1. Field of the Invention
The present invention relates to a honeycomb extrusion die for extruding a ceramic honeycomb body and a method of manufacturing the same. Especially, the present invention relates to a honeycomb extrusion die and a method of manufacturing the same, in which a honeycomb structural body having a small pressure loss and a predetermined strength can be extruded in an accurate shape without transforming its shape during extruding.
2. Related Art Statement
Generally, as a honeycomb extrusion die for extruding a ceramic honeycomb body, a honeycomb extrusion die is known in which a plurality of intersection slits formed by cell blocks are arranged in a front surface thereof and a plurality of raw material holes communicated with the slits are arranged in a block surface thereof. As one example of the honeycomb extrusion die, the applicant proposes a technique in Japanese Patent Publication No. 61-39167 (JP-B-61-39167) in which each of the cell blocks has a round portion formed at corners thereof. Moreover, there is a technique in Japanese Patent Laid-Open Publication No. 60-145804 (JP-A-60-145804) in which each of the cell blocks is formed by coating iron boride, chromium carbide, aluminum oxide, titanium carbide, titanium nitride or titanium nitride carbide on a cell block body by means of chemical vapor deposition (CVD).
Recently, in order to meet a severe exhaust gas regulation or to improve exhaust gas purifying properties and honeycomb article properties, there is a requirement such that a ceramic honeycomb structural body after extrusion has a thin cell wall such as 45-120 .mu.m which is thinner than the known cell wall thickness. Also, there is a requirement such that a honeycomb extrusion die for extruding a ceramic honeycomb body having such a thin cell wall and a method of manufacturing the same are developed.
However, in the technique disclosed in JP-B-61-39167 in which a slit width is controlled by electroless plating layer, there is a drawback such that a honeycomb extrusion die which can extrude a ceramic honeycomb structural body having a thin cell wall such as 45-120 .mu.m is not obtained, if this technique is applied as it is.
Moreover, in the technique disclosed in JP-A-60-145804 in which a slit width defining a thickness of cell wall is controlled by chemical vapor deposition (CVD) layer, there are following drawbacks. That is to say, a thick coating layer is not formed only by CVD coating, and it is at most 30 .mu.m as shown in JP-A-60-145804. Therefore, it is necessary to preliminarily work a metal block by means of for example electrical discharge machining or grinding so as to form a slit having a relatively small width. However, even if a thickness of CVD coating layer for finally controlling a slit width takes into consideration, it is not possible to perform such a preliminarily slit working only by the known electrical discharge machining or grinding. Moreover, it is not possible to form a round portion at corners of each of the cell blocks defining the slits only by CVD coating technique.